In the security and surveillance field, it is common practice to monitor rooms or other areas of interest with pan-tilt-zoom ("PTZ") cameras. Generally a PTZ camera is mounted in a transparent dome above or on the ceiling of the area of interest. The camera usually is a closed-circuit television camera. The camera is controlled remotely or automatically in order to view regions of interest within the room.
While such cameras can view any region, area of interest, or target, they have a relatively narrow field of view, and cannot see all regions at once. To view a different region of interest, the camera is commanded to pan, tilt, and/or zoom as necessary to bring the new region of interest into view. The process of panning, tilting, and/or zooming to the new region of interest or target takes time, and when the camera is viewing the new region or target, it can no longer see the original region. This limits the effectiveness of such cameras, since activities can only be monitored, recorded or tracked in one area at a time. Unmonitored areas are subject to unmonitored intrusions.
Omnidirectional imaging systems have been developed which permit simultaneous viewing and image capture of an entire room. These systems employ an image sensor that is mounted to receive light rays reflected from a wide-angle reflector, such as a parabolic mirror, in order to capture an omnidirectional, often hemispherical image. Embodiments of omnidirectional imaging systems are described in U.S. patent application Ser. No. 08/644,903, entitled "Omnidirectional Imaging Apparatus," filed May 10, 1996.
One significant drawback of such omnidirectional imaging systems is that they provide only a wide-angle view of the area of interest. Because of the large viewing angle used to provide the wide-angle view, the resulting image has limited resolution. For example, when a video camera is used to capture a video image of a large room using a wide-angle view, a relatively small number of pixels of the video display are used to display each region of the room. Consequently, it is hard to make out details of the area of interest or to locate small objects. Further, the camera is fixed with respect to the wide angle optical system. As a result, a video image generated from the image sensor's signal shows the room or area of interest only from the viewpoint of the wide-angle reflector, and the views of the room have relatively low resolution.
Omnidirectional cameras also have been developed using fisheye lenses to capture wide, panoramic images.
However, the resolution of the images produced by all the above-described systems is limited by the fact that the field of view is projected onto a sensor which is typically used to generate an image for a much narrower field of view. For example, a conventional sensor might produce an image on a computer display screen having 640.times.480 pixels. Similar levels of resolution are supported by broadcast standards such as NTSC and S-video. Sensors with higher resolution are unusual and are very expensive; one reason is that it is difficult to capture and transmit the large amount of image data involved in real time. Hence, the number of pixels of the sensor that is available for any particular region in the image is relatively small, especially for omnidirectional systems with very wide fields of view.
Another approach to wide field of view imaging, typically used for still frame photography, is the rotating panoramic camera, as exemplified by the Kodak Roundshot.TM.. Cameras of this type take still frame exposures of several different but contiguous regions in sequence, and then concatenate them to form a panoramic image. Each exposure typically appears as a thin strip of the final image. Since these cameras take multiple exposures, obtaining a complete panoramic image takes on the order of several seconds. Accordingly, they are useful typically in the still frame area only, rather than video or real-time surveillance applications, in which high frame rates are necessary.
Based on the foregoing, there is a clear need for an optical system that can provide both a wide-angle view of an area of interest, and a close-up view of a particular region within the area of interest, using a single image sensor.
There is also a need for an optical system that can provide both a wide-angle view of an area of interest and a narrower view of a particular region within the area of interest, using a single image sensor, while maintaining registration between the wide field of view and close-up view when the image sensor is moved from the wide-angle view to a narrower view. There is also a need for an optical system that fulfills the foregoing needs and can be remotely controlled to carry out movement from the wide-angle view to the narrower view.
There is also a need for an optical system that fulfills the foregoing needs and can be automatically controlled to carry out movement from the wide-angle view to the narrower view.